Theretofore, there has been known an infrared reflective substrate configured by disposing an infrared reflective layer on a backing such as glass or film. As the infrared reflective layer, a laminate obtained by alternately laminating a metal layer and a metal oxide layer is widely used. It functions to reflect near-infrared rays such as solar light to thereby impart heat insulating property. As the metal layer, silver or the like is widely used, from a viewpoint of enhancing a selective reflectivity in the infrared region. As the metal oxide layer, indium tin oxide (ITO) is widely used. The metal layer and the metal oxide layer are not sufficient in terms of physical strength such as abrasion-resistant. Moreover, they are apt to undergo degradation due to external environmental factors such as heat, ultraviolet rays, oxygen, water and/or chlorine (chloride ions). In view of this, generally, a protective layer is provided on the infrared reflective layer on a side opposite to the backing.
In late years, it has been attempted to reduce an emissivity of an infrared reflective film to provide enhanced heat insulating property. A key point for reduction in emissivity of an infrared reflective film is to effectively reflect far-infrared rays toward an indoor pace by a metal layer in an infrared reflective layer of the infrared reflective film. However, a film or a curable resin layer (hard coat layer) used as a protective film of the infrared reflective film generally contains a large amount of a compound comprising a C═C bond, a C═O bond, a C—O bond and an aromatic ring, and therefore exhibits large infrared vibrational absorption in a wavelength range of 5 μm to 25 μm within a far-infrared region. Far-infrared rays absorbed by the protective layer are thermally diffused toward an outdoor space by heat conduction, without being reflected by the metal layer. Thus, when an amount of far-infrared rays absorbed by the protective layer becomes larger, the emissivity of the infrared reflective film increases, resulting in failing to obtain a heat insulating effect.
With a view to reducing emissivity of an infrared reflective film, the following Patent Document 1 proposes a technique of reducing an amount of far-infrared rays to be absorbed by a protective layer, wherein a cured material layer such as cured fluorosilane is used as a transparent protective layer, and a thickness of the cured material layer is set to be equal to or less than 500 nm.